The following measures are known for implementing a socalled “safe robot”:                limiting the axis or axle speed by software restriction;        limiting speeds by restricting the intermediate circuit strain;        monitoring the speed and/or position via several redundant monitoring channels;        collision monitoring by monitoring the drive moments via the motor currents;        collision monitoring by separate sensor systems, e.g. for detecting an approach to obstacles (capacitive, in ductive, ultrasonic, visual) or contact forces (pressure measuring mats with different physical principles);        exclusion of specific parts of the operating area by mechanical stops or by software.        
In part the indicated measures are not safe as the sole measures, but only fulfil this requirement in conjunction with at least one further monitoring channel and in part they are complicated and costly. Thus, generally through a multichannel system, i.e. monitoring and making use of several measurements an adequate redundancy is provided. Moreover, up to now even a redundant monitoring has involved identical or related measured quantities solely being detected by two or more sensors in the form of measured values, which are transmitted and processed by means of separate channels, so that it was only possible to eliminate errors in the detection, transmission and processing, but not with respect to the detected measured or physical quantities.
The problem of the invention is to improve the monitoring of a machine, such as an industrial robot, in order to increase safety.